Recently, a construction machine such as a hybrid excavator is employed which is equipped with a swing apparatus that swivels an upper swing structure with respect to a lower traveling structure using an electric swing motor driven by electric energy.
As shown in FIG. 1, a swing control system for a hybrid construction in accordance to the prior art includes:
a swing manipulation lever (not shown) that outputs a swing manipulation signal that is proportional to a manipulation amount by an operator;
an electric swing motor 1 that is driven in response to an electric control signal corresponding to the manipulation amount of the swing manipulation lever to cause an upper swing structure to be swiveled with respect to a lower traveling structure;
a speed detection sensor 2 that detects a rotational speed of the swing motor 1;
a controller 3 that calculates a driving speed of the swing motor 1 based on the swing manipulation signal by the manipulation of the swing manipulation lever and a rotational speed detection signal, which is fed back thererto from the speed detection sensor 2;
an inverter 4 that converts DC into AC in response to a control signal, which is applied thereto from the controller 13, and applies the converted AC power to the swing motor 1 to drive the swing motor 1.
When the swing manipulation signal according to the manipulation of the swing manipulation lever by the operator and the rotational speed detection signal, which is fed back thererto from the speed detection sensor 2, are applied to the controller 3, the controller 3 can calculate a driving speed of the swing motor 1 based on the swing manipulation signal and the rotational speed detection signal to cause the swing motor 1 to be driven based on a current value for control applied to the inverter 4 from the controller 3.
Meanwhile, as in a loading work using an excavator, during a combined operation in which the swing operation of the machine and the driving operation of the work apparatus including a boom and the like are performed, the swing inertia of the machine varies depending on a change in position of the work apparatus, leading to a change in the swing acceleration of the machine.
In this case, as shown in FIG. 2, the swing acceleration a of the machine is in inverse proportion to the swing inertia J of the machine ((J∝1/α). This becomes an obstacle factor to maintain repeatability of the swing operation, resulting in a deterioration in the workability in the case where the operator performs the combined operation of the machine and the work apparatus.